1. The Field of the Invention
The present invention relates to the restoration of computer data, and more particularly to a system and method for restoring data on a primary mass storage system through the use of a secondary mass storage system, while optimizing user access to the data from the time that the data is lost until it is restored to the primary mass storage system.
2. Background and Related Art
Businesses worldwide recognize the commercial value of data stored on their computer systems and are continually seeking reliable, cost effective ways to protect their valuable data. One common technique for protecting data is to make a backup copy of the data on a remote server so that the data can be retrieved if, for any reason, the original copy of the data is damaged or destroyed, such as for example, by a fire, flood, earthquake, explosion, or any other disaster. The effectiveness of this technique, however, depends, at least in part, on separating the remote server a significant distance away from the primary server, so that the event(s) causing damage to the original data will not also damage the backup data.
One consequence of separating the remote server from the primary server is that the available and affordable communication data rate between the two servers is significantly less than it would be if the servers were in close proximity. Accordingly, the loss of valuable data from a computer system may require an exorbitant amount of resources and time to be expended in order to restore the lost data to the computer system.
The costs associated with restoring data, which arises from not being able to use the computer system while data is being restored, are becoming greater as companies increasingly rely on computers and computerized data. Some companies have become so dependent on computerized data that the technique of shutting down the computer system for updates or data restoration is prohibitively expensive. This is particularly true when updating the data requires the computer system to be shut down while a backup tape is transported to the local site and until a mirrored copy of the data concurrently exists at the local and remote site.
Even when data is transmitted through high bandwidth communication lines, slow data rates resulting from the distances between the local and remote sites can extend the remirroring times between servers from hours to days or longer because of today's large data storage sizes. Further complicating the issue, during a remirror, data is copied on a physical block basis rather than a logical file basis. Accordingly, if the remirror is not 100% completed, the data is virtually worthless. Hence, during the remirror period, only a single copy of the data exists, during which time the data is vulnerable to becoming permanently lost or damaged.